The present invention ensures air tightness and waterproof performance at a cord insertion hole formed in a back cover for replacing a light source bulb that is mounted at a rear apex portion of a lamp body. The lamp body is a basic component member of a lamp for a vehicle such as an automobile or a motorcycle.
More particularly, the present invention relates to an improvement of a lamp body back cover structure to ensure air tightness and waterproof performance at the cord insertion hole. A cylindrical outer wall is formed around the cord insertion hole in the back cover, filled with a soft synthetic resin and cured in the outer wall, and a power supply cord inserted in the cord insertion hole is fixed by the resin mold portion inside the outer wall.
In general, a back cover for light source bulb replacement is engagingly fixed to a light source bulb insertion opening formed at the rear apex of a generally cup-shaped lamp body that forms a housing of a vehicle lamp such as a headlamp for an automobile or motorcycle.
Conventionally, one or a plurality of power supply cords for supplying current from a power source to a light source bulb disposed inside the housing are inserted and fixed to the back cover for a lamp body. A variety of constructions have been proposed for ensuring air tightness and waterproof performance of the gap formed at the power supply cord insertion portion.
Such constructions typically include, a first construction, as shown in FIG. 4(a), wherein all power supply cords 21a, 21b for supplying current to a light source bulb, not shown, are inserted and fixed to a rubber bushing 22. This rubber bushing 22 is fitted into a predetermined hole 23 formed in a back cover 20a that is engagingly fixed to a lamp body 21. A second construction, which is an improved configuration, is shown in FIG. 4(b), wherein two cord insertion holes 25a, 25b corresponding to the respective power supply cords 21a, 21b are provided in a back cover 20b (partially shown) at intervals, cylindrical protrusions 26a, 26b are provided so as to surround the respective insertion holes 25a, 25b, small rubber bushings 24a, 24b having power supply cords 21a, 21b inserted and fixed therein in advance are fitted into the respective inner regions of the protrusions 26a, 26b, and adhesives 27a, 27b are poured from above the small bushings 24a, 24b so as to provide a seal.
However, in the first construction mentioned above, the engagement areas between the bushing 22 and the cord insertion hole portion, and between the bushing 22 and the back cover hole 23 tended to be large due to the relatively large bushing 22 used therein. Also, sufficient air tightness and waterproof performance are not obtained due to a difference in material of the rubber bushing 22 and the synthetic resin back cover 20a. Further, technical problems existed such as that fitting the bushing required some effort and automation was not possible.
In the second construction, the assembly work (installing the power supply cord) required a step for inserting and fixing a power supply cord 21 to a bushing 24, a primer processing step for the lamp body, a step for inserting the bushing 24, and a step for filling an adhesive 27. This resulted in a large number of working man hours. Further, there existed technical problems such as that the fixing force of the power supply cord 21 is weak due to the fact that the adhesive 27 is filled from above the bushing 24.
The present invention has been devised in order to solve the drawbacks of the prior art. Particularly, the present invention provides a back cover for a lamp body that ensures air tightness and waterproof performance at the power supply cord insertion location in the back cover for a lamp body of a vehicle lamp, while reducing man hours required for fixing the power supply cord to the back cover.
Means described hereunder are adopted in order to achieve the above-mentioned result.
In the back cover for a lamp body first, a cylindrical outer wall protrudes from a back face of the back cover so as to surround the cord insertion hole for inserting the power supply cord that supplies current to the light source bulb. Then, a soft synthetic resin (hot melt resin) is filled inside a space formed by the outer wall, and the power supply cord is inserted in the cord insertion hole and fixed and integrated by this resin mold portion. The resin mold portion has such a structure that an upper mold layer with good heat resistance is laminated over a lower mold layer on the cord insertion hole side that adheres well to the back cover. With this means, the structure is such that no bushing member is used in inserting and fixing the power supply cord to the back cover. Accordingly, the steps of inserting the power supply cord with respect to the bushing or installing and fixing the bushing can be eliminated. As a result, the number of man hours required to install the power supply cords can be reduced and the work automated while air tightness and waterproof performance can be ensured with a simple method of plugging the cord insertion hole portion with a synthetic resin. Also, since the resin mold portion has such a structure that an upper layer with good heat resistance and high rigidity is laminated over and integrated with a lower mold layer on the cord insertion hole side that adheres well to the back cover, generation of creep in the resin mold portion (lower mold layer) is prevented by the upper mold layer having good heat resistance and high rigidity, whereby adhesion between the lower mold layer and the back cover is maintained. Further, to form a layer-structured resin mold portion, first, a soft synthetic resin (hot melt resin), for example, for the lower mold layer is filled. After it has cured to some extent, a soft synthetic resin (hot melt resin), for example, for the upper mold is filled and cured. In the back cover for a lamp body, the back cover may be made of polypropylene, the lower mold layer may be made of an olefin or synthetic rubber based hot melt agent, and the upper mold layer may be made of a polyamide based hot melt agent, respectively. The olefin or synthetic rubber based hot melt agent that forms the lower mold layer on the cord insertion hole side adheres well with the polypropylene back cover. The upper mold layer made of polyamide hot melt agent laminated over and integrated with the lower mold layer adheres to the lower mold layer, has good heat resistance, reliably prevents the generation of creep in the lower mold layer, and reliably maintains the adhesion of the lower mold layer with the back cover. A back cover for a lamp body may be structured such that a ratio of a thickness of the lower mold layer and a thickness of the upper mold layer is 2 to 1. Since the thickness of the lower mold layer that adheres well to the back cover is twice that of the upper mold layer, adhesion in a region two thirds of an adhesion area with the outer wall on the lower layer side of the resin mold portion is maintained. With the back cover for lamp body, the power supply cord may be coated with a polyethylene based resin. The polyethylene based resin (coated portion of the power supply cord) adheres well to the olefin or synthetic rubber based hot melt agent that forms the lower mold layer on the cord insertion hole side, and adhesion of the lower mold layer to the back cover and the power supply cord is maintained.
Now, preferred embodiments of the present invention will be described with reference to the attached drawings.